The present invention relates to a method of regulating the tension of warp yarns in a loom or weaving machine.
In a conventional method of regulating the warp yarns delivered from a warp beam in a weaving machine so as to maintain the tension thereof within a predetermined range, the variation of the warp yarn tension is monitored constantly by a detecting member such as a tension roller movable with a change in the tension of the warps, and the speed at which the warp yarns are unwound from the warp beam is increased when the tension is built up to exceed the upper limit of the permissible range while the speed is decreased when the tension is dropped below the lower limit of the range, thus providing automatic regulation of warp yarn tension during weaving operation of the loom.
A typical arrangement for controlling the warp yarn tension in a weaving machine or a loom is exemplified in FIG. 1, wherein a tension roller 1 which is attached at one end of a tension lever 4 rotatable about a stationary shaft 30 is caused to move up and down in response to the change of tension in the warp yarns Y which are unwound from a warp beam 2 and passed over a back roller 3 and then over said tension roller 1. This motion of the tension roller 1 is transmitted to a speed change control lever 7 of a speed change device or a speed reducer 6 through a link 5 which is articulated at one end thereof to the other end of the tension lever 4 and at the opposite end thereof to said control lever 7. The speed reducer unit 6, which reduces the output speed of a main motor M of the loom and drives the warp beam 2 at a reduced speed, can change its speed change ratio or reduction ratio in accordance with the displacement of the tension roller 1. In FIG. 1, reference symbol W denotes a counterweight which acts to urge the tension lever 4 to rotate in clockwise direction (as viewed in FIG. 1) about the shaft 30 for providing a desired tension to the warp yarns Y; reference numeral 8 designates the shaft of the warp beam 2; reference numeral 9 designates a shed formed by upper and lower sheets of warp yarns; and numeral 10 indicates a cloth roller which is driven by the main motor M for winding up at a constant speed V a woven fabric or cloth C guided by a guide roller 11.
In the above arrangement for regulating the warp yarn tension, when the tension of the warp yarns Y is increased to exceed the upper limit of a predetermined range, the tension roller 1 is moved downwards against the action of the counterweight W to lift the speed change control lever 7 slightly, thereby adjusting the reduction ratio of the reducer 6 in such a way that the speed at which the warp yarns Y are fed out from the warp beam 2 is increased; while in case of a decrease in warp yarn tension below the lower limit of the range, the tension roller 1 is displaced upwards slightly, thus decreasing the warp yarn feeding speed.
In the event that a weft yarn fails to be picked properly through a shed in a weaving machine as described in the above and therefore there is a need to remove that weft yarn to prevent formation of a defect in the resulting cloth C, it is necessary to drive the main motor M in its reverse direction after it has been stopped automatically in response to the above-mentioned failure in weft yarn insertion. Driving the motor M in reversed direction reverses the weaving machine so that the weft yarn held by the warp yarns Y is released and may be pulled out from the cloth C. Accordingly, the cloth beam 10 is then rotated reversely, too, in conjunction with the reversing operation of the main motor M. Should the warp beam 2 then be rotated in its forward direction while the cloth beam 10 is reversed, the warp yarns Y being unwound therefrom would be slackened so greatly that the quality of the cloth C being woven would be seriously affected. In order to avoid such excessive slackening of the warp yarns Y during reversed operation of the weaving machine, the reduction unit 6 is so constructed that it drives the warp beam 2 in either direction in accordance with the rotation of the main motor M of the machine, or any suitable reversing mechanism is provided between the reduction unit and the warp beam when the former is constructed otherwise so that it can be operated in forward direction only.
In the arrangement for warp yarn tension regulation which includes a reduction unit which may thus drive the warp beam 2 in reverse direction, however, if the machine is operated in reverse direction when the warp yarns Y are in a relatively slackened state, or when the speed v at which the warp yarns are unwound from the warp beam 2 is higher than the speed V at which the cloth C is taken up by the cloth roller 10 during forward operation of the loom, then the speed at which the warp yarns Y are rewound by the warp beam 2 will become greater than the speed at which the cloth C is unwound from the cloth roller 10. This means that the warp yarns will be tensioned greater than they were before reversing the loom. Then, the tension roller 1 will be moved downwards by the increasing warp yarn tension to lift the control lever 7, with the result that an adjustment will be made by the speed reducer 6 in such a way that the rotational speed of the warp beam 2 will be further increased. That is, the reduction ratio of the speed reducer 6 is adjusted during such reversed rotation of the weaving machine in such a direction that the speed at which the warp beam 2 is rotated for rewinding of the warp yarns Y is increased, in spite of the need that the rotational speed of the warp beam should be decreased for slowing down the warp yarn rewinding by the warp beam adjust for the increase of warp yarn tension. If the machine continues to be reversed further, adjustment of the reduction ratio of the speed reducer 6 will be promoted further in the wrong direction.
On the other hand, if the loom is operated in reverse rotation when the warp yarns Y are in a relatively tightened state, or when the speed v of the warp yarns is lower than the speed V of the cloth C during forward operation of the loom, then the speed at which the warp yarns are rewound by the warp beam 2 will become less than the speed at which the cloth is unwound from the cloth roller 10. This means that the warp yarns Y will be slackened to a greater extent than they were before the loom was reversed. Consequently, the tension roller is moved upwards by the decreasing warp yarn tension to lower the control lever 7, with the result that an adjustment is made by the speed reducer 6 in such a way that the rotational speed of the warp beam 2 is further decreased. In other words, the speed change ratio of the speed reducer is adjusted during such reversed operation of the weaving machine in such a direction that the speed at which the warp beam 2 is rotated for rewinding the warp yarns Y is decreased, in spite of the need that the rotational speed of the warp beam should be increased for increasing the speed of warp yarn rewinding by the warp beam to adjust for the decrease of the warp yarn tension. If the machine continues to be reversed further, adjustment of the reduction ratio of the speed reducer will be promoted further in the wrong direction.
As a disadvantage resulting from the above-described situations, extremely troublesome and time-consuming adjustments for the cloth fell position and speed reduction ratio of the speed reducer 6 should be made prior to restarting the loom in its normal forward rotation for preventing formation of weaving defects such as weft bar which may be produced in the cloth C in restarting the loom subsequent to its reversing operation.
Furthermore, because the adjustment of the speed change ratio of the reduction unit 6 is moved to a greater extent in the wrong direction if the loom is continued to be reversed for a prolonged period of time, the above disadvantage becomes more pronounced when reversing the weaving machine for any relatively long time duration for remedying any weaving defect in the cloth.